This chapter covers
- The definition of a LAN
- The contents of the Ethernet header and trailer
- How switches learn the MAC addresses of devices in the network
- How switches forward frames to the appropriate destination
- How network hosts use ARP to learn the MAC address of other hosts
- The ping utility
In this chapter, we will cover Ethernet LAN switching, which is the process switches use to forward frames to their proper destinations within a LAN. A frame is a Layer 2 PDU, including the Layer 2 header, trailer, and payload; we covered PDUs in chapter 4. When a network host sends a frame out of its port, it is the switch’s role to make sure the frame reaches its proper destination.
This chapter covers material from domain 1.0 of the CCNA exam topics: Network Fundamentals. Specifically, we will cover the following topics:
- 1.13 Describe switching concepts
- 1.13a MAC learning and aging
- 1.13b Frame switching
- 1.13c Frame flooding
- 1.13d MAC address table
It is often said that switches are Layer 2 devices or that they operate at Layer 2. The reason for this is that switches use information in the Layer 2 header (the Ethernet header) to make forwarding decisions. This is in contrast to routers, which use information in the Layer 3 header (the IP header) to make forwarding decisions. We will cover how routers forward network traffic between LANs in part 2 of this book, but for now, we will focus on how switches forward traffic within a LAN.